Origin of the Mizab barite vein-type deposit, Ain Mimoun (NE Algeria): evidence from fluid inclusion and S-, O- and C-stable isotope studies

Zedam, R., Laouar, R., Lekoui, A., Metrouni, H., Bouhlel, S., Boyce, A. J. and Fallick, A. E. (2022) Origin of the Mizab barite vein-type deposit, Ain Mimoun (NE Algeria): evidence from fluid inclusion and S-, O- and C-stable isotope studies. Arabian Journal of Geosciences, 15(3), 298. (doi: 10.1007/s12517-022-09611-4)

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The Khenchela massif, northeast Algeria, belongs to the eastern Saharan Atlas that extends northeasterly from the Aurès Chain, through the Mellegue mountains, to the Tunisian Atlas. This massif is characterized by sandstone and marl outcrops of the Lower Cretaceous that are overlain by limestone and marl of the Upper Cretaceous. The anticline structure was subjected to several NW–SE to WNW-ESE-directed major normal faults that split the massif into a number of mega-blocs. Triassic evaporitic lithologies crop out as diapirs at the northeastern and southwestern parts of the anticline. The Ain Mimoun region, located on the northern flank of the Khenchela anticline, is composed of Albian-Aptian sediments that host the barite veins of the so-called ‘Mizab barite deposit’. This deposit, which is currently exploited, consists of a dozen main veins composed mainly of barite with quartz, calcite, ankerite and rare base-metal sulphide mineralisation (galena, sphalerite, tennantite and chalcopyrite). The host sedimentary rocks were subjected to severe silicification and dolomitisation processes. Barite shows a number of aspects: banded, massive and stockwork; in all cases, barite shows tabular crystals of several millimeters in size. Microthermometric measurements carried out on primary two-phase fluid inclusions in barite crystals (barite I and barite II) and gangue quartz gave homogenization temperatures between 155 and 225 °C and salinities of 17.6 to 25.9% NaCl eq. The data show at least three types of mixing fluids that deposited the sulphate-sulphide mineralisation. δ34S values of barite are between + 17.9 and + 27.6‰ and the δ34S values of the associated sulphides vary between − 9.2 and + 3.0‰. These data indicate that the most likely source of sulphur is the sulphates (gypsum) of the Triassic evaporitic formation (δ34S ranging between + 11.5 and + 13.4‰). Thermochemical sulphate reduction is the most probable process by which H2S was produced, although relatively large negative δ34S values point to a possible minor contribution from the biogenic sulphate reduction process. Carbon and oxygen isotopic compositions of gangue carbonates (calcite and ankerite) and oxygen of gangue quartz indicate a common source of the mineralising fluid. Calculated δ18Ofluid from quartz oxygen isotope data varies between + 6 and + 12‰, indicating deep-seated brines with minor contribution from a surface water component. The relatively hot and saline fluids have most likely migrated upward in several pulses during the Triassic halokinesis and compressive/distensive Atlassic (Eocene) and Alpine (Miocene) tectonic phases. The Mizab barite deposit exhibits geological, fluid inclusion and isotopic features similar to those of the peridiapiric mineralisation of northeastern Algeria and Tunisia.

Item Type:Articles
Additional Information:Funding SUERC is funded by NERC and the Scottish Universities Consortium. They also received isotope analyses technical support from T. Donnelly, A. Tait, C. Taylor and J. Dougans. A.J. Boyce is funded by NERC support of the Isotope Community Support Facility at SUERC.
Glasgow Author(s) Enlighten ID:Fallick, Professor Anthony and Boyce, Professor Adrian
Authors: Zedam, R., Laouar, R., Lekoui, A., Metrouni, H., Bouhlel, S., Boyce, A. J., and Fallick, A. E.
College/School:College of Science and Engineering > Scottish Universities Environmental Research Centre
Journal Name:Arabian Journal of Geosciences
ISSN (Online):866-7538
Published Online:02 February 2022

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